1. Field of the Invention
The present invention relates to a heating appliance and, more particularly, to a direct fired heating appliance suitable for outdoor use.
2. Description of the Invention Background
A variety of direct fired heating appliances have been developed and are commonly used to heat fluids, such as water or glycol, or gasses, such as air. The term "direct fired" typically indicates that fuel is burned directly within the heater to create heat which is used to warm a desired medium. In one application, a direct fired heater is utilized to warm water in a swimming pool or spa. A typical heater employed to heat pool or spa water includes a burner assembly and a heat exchanger assembly enclosed in a housing.
A typical burner assembly includes a burner subassembly, a fuel distribution assembly and an igniter. Fuel is supplied to the fuel distribution assembly through a fuel supply line. The fuel is regulated and distributed to the burner subassembly through the fuel distribution assembly. The fuel distribution assembly is typically comprised of a fuel valve and regulator, which are often combined into a single unit, and a fuel manifold.
A conventional fuel valve and regulator unit typically has an inlet port for connection to a fuel supply line, an outlet port for connection to the fuel manifold, a twoposition flow control member with an actuator that may be manipulated to position the flow control member to either permit or prevent the flow of fuel through the valve and a regulating flow control member that is modulated to maintain a constant fuel flow rate. A conventional fuel manifold includes an inlet port that is connected to the fuel valve and regulator and a plurality of coupling members having orifices and barbs for connection to a burner.
A conventional burner subassembly includes a plurality of burner elements and a rack supporting the elements. Each burner element is connected to a fuel manifold coupling member and held in place by the barb of the coupling member. Various fuels, such as propane and natural gas, may be burned in a typical heater and fuel manifolds typically must be configured differently for each fuel. For example, the orifice size may vary depending on the thermal properties of the fuel and the pressure at which the fuel is delivered so that the designed amount of heat is produced in the heater.
While conventional fuel manifolds can effectively distribute fuel to a burner, a shortcoming of such manifolds is that they are not easily replaced. The barbed coupling members of a conventional fuel manifold engage the burner such that disengagement is difficult and may be damaging to the fuel manifold or burner. Thus, when a manifold becomes damaged or a new fuel is desired to be utilized, conventional burner and manifold assemblies are typically replaced in their entirety. Therefore, there is a need for a replaceable fuel manifold.
A conventional burner consists of a series of burner elements arranged in a frame such that combustion air may flow around the burner elements. Each burner element typically has a fuel supply port to which is connected one of the barbed coupling members of the fuel manifold and through which the fuel enters the burner element. A typical burner element, furthermore, includes a series of openings along its upper surface through which the fuel flows and at which point the fuel is burned.
An igniter is situated above the burner to ignite the fuel flowing through the openings in the elements of the burner. A conventional igniter may be a standing pilot or an electronically controlled ignition system.
A conventional heat exchanger includes a tube subassembly, a primary manifold and a secondary manifold. The heat exchanger is typically located above the burner such that heated air rising from the burner becomes incident on the exterior surfaces of the heat exchanger. The heat exchanger may also contain baffles around the tube subassembly that direct the heated air against the tube subassembly to maximize heat transferred to the pool water. A conventional tube subassembly is comprised of a series of heat conducting tubes disposed in parallel with each end of each tube connected to a manifold. The purpose of the tube subassembly is to transfer heat from a high temperature medium to a low temperature medium while preventing the high and low temperature mediums from contacting each other. To accomplish that heat transfer in such a tube assembly, either the high or low temperature medium is forced through the heat conductive tubes while the other medium is forced to flow past the external surfaces of the tubes in contact therewith. When the high temperature medium contacts the lower temperature tubes, heat is transferred from the high temperature medium to the tubes. Likewise, heat is transferred from the tubes to the lower temperature medium as the low temperature medium contacts the tubes. Thus, heat from the high temperature medium is transferred through the heat conductive tubes to the lower temperature medium.
A typical housing for a direct fired heating appliance is a four sided enclosure with a combustion air inlet near the bottom of one side and a combustion air outlet at its top. The burner assembly may be supported by the housing above the combustion air inlet, and a heat exchanger assembly may be supported by the housing above the burner assembly. The space generally between the burner assembly and heat exchanger assembly is referred to as the "combustion chamber."
In operation, a pressurized fuel is present in the fuel supply line and at the fuel valve. When heater operation is desired, the fuel valve is opened, permitting the fuel to flow into the manifold. Thereafter, the pressurized fuel flows through the orifices of the manifold into the burner elements and out of the burner elements through the burner openings where the fuel is ignited and consumed, thereby heating the air in the combustion chamber.
Combustion air is concurrently circulated through the heater, typically flowing in through the bottom of the heater, up past the burner, through the heat exchanger and exiting through the top of the heater. Purposes of circulating combustion air through the heater include providing oxygen to assist in combustion, preventing the build-up of products of combustion in the heater, and carrying heat created by the burning fuel to the heat exchanger.
A continuous supply of oxygen-rich combustion air must be provided to the combustion chamber in order to promote thorough, efficient burning of all fuel. Adequate air circulation through the heater is also necessary to prevent the heater from being damaged by overheating. Adequate air circulation also prevents the build-up in the appliance of oxides of nitrogen, carbon monoxide, and other products of combustion that may damage the appliance or may be hazardous to humans.
The combustion air in the combustion chamber is also heated by the burning fuel. The heated air rises through the combustion chamber, contacting the heat exchanger and transferring heat from the air, through the heat exchanger to the pool or spa water. After passing across the heat exchanger, the heated air, or "flue gas," is vented out of the heater.
A certain pool heater utilizes a natural drafting system, which relies on the buoyancy of heated flue gasses to circulate air through the heater. In such a system, air in the combustion chamber is heated, thereby becoming more buoyant than the ambient air. The buoyant flue gasses rise through the heat exchanger and out of the housing, evacuating the combustion chamber. Fresh combustion air is drawn into the combustion chamber through a lower opening in the housing to replace the escaping flue gasses. In that way air is circulated through the pool heater, entering through a lower portion of the housing and leaving through an upper portion of the housing.
Natural draft systems must, however, balance the opposing goals of transferring heat from the flue gasses to the pool water and permitting flue gasses to be vented at a temperature high enough to create adequate air circulation. The result is that natural draft systems waste energy because the flue products must be maintained at a high temperature to insure that air circulation is adequate to prevent heat damage to the heater and to prevent the buildup of hazardous products of combustion.
In outdoor applications, the use of natural drafting appliances is also problematic because wind may overcome the natural draft created by the heated flue gasses, thereby preventing proper air circulation through the appliance. In certain natural draft appliances, baffles are used to isolate the flue gasses from wind and to create alternative venting paths. The alternative venting paths limit the effect of wind by providing paths from which the gasses may be exhausted when ambient pressure exceeds flue gas pressure at certain paths and prevents the flue gasses from venting at those paths. The baffles, however, restrict airflow both by the friction of the air against the many baffle sections and the redirection of the air by the baffles, thereby reducing, rather than improving, circulation through the appliance. Appliances so constructed often experience poor combustion, soot build up and a tendency for flames to roll out of the appliance.
Another heating appliance utilizes a supply fan disposed at the combustion air intake to circulate combustion air through the heater. The supply fan provides pressurized air to the combustion chamber. The pressurized air propels the flue gasses out of the appliance with a force that will typically overcome the effects of wind, insuring that proper draft is maintained through the appliance. The pressurize combustion chamber, however, creates a potential for flames to escape from the appliance should the combustion chamber become breached. Another result of the pressurized combustion chamber is that a direct, unrestricted pathway must be provided at the exit of the heater to prevent overpressurization of the combustion chamber. A heater utilizing a supply fan is subject to the effects of rain because of the direct exhaust pathway and so is not well suited to outdoor use.
Certain other heating appliances utilize a venting fan disposed at the flue gas vent to circulate combustion air through the heater. The venting fan is intended to draw flue gasses out of the appliance and to create negative pressure in the appliance sufficient to draw combustion air into the combustion chamber from the combustion air inlet. The venting fan also expels the flue gasses from the appliance under pressure that will typically overcome the effects of wind. Venting fans are typically even more costly than combustion air fans because they must be designed to operate under high temperature conditions. Venting fans may also create turbulence in the combustion chamber which can adversely affect combustion. When used in outdoor applications, the venting fan should be protected from rain and other precipitation, necessitating the use of a cover. Certain previous venting fan covers, however, have prevented free passage of flue gasses out of the appliance, resulting in the collection of corrosive condensation from the flue gas on components of the appliance. A need, therefore, exists for an efficient, long lasting heating appliance that provides proper combustion air circulation.
In conventional heaters having both natural and fan-induced draft systems, high temperatures are typically experienced in and around the heater due to heat transfer from the combustion chamber through the housing. Combustion and electrical components that may be utilized to control operation of the heater are typically disposed on or near the housing. Exposure of these components to the high temperature of the heater is damaging to and reduces the operational life of the components. Furthermore, an appliance that loses excessive heat through its housing may be inefficient. Additional fuel must be expended and a larger heating appliance may be required to induce the same heat gain in the pool water when heat is lost to the atmosphere rather than transferred into the pool water. An excessively hot housing also poses a risk to people and property in the vicinity of the appliance. Therefore, a need also exists for a heater that prevents exposure of combustion and electrical components to high temperatures and recovers heat from the housing.
Thus, there is a need for a heater that may be more easily serviced, offers improved combustion emissions, has cooler external surface temperatures and has a longer service life.